Compressor arrangement



1965 D. K. EMMERMANN ETAL 3,202,343

COMPRES 5 OR ARRANGEMENT Filed May 16, 1962 5 Sheets-Sheet 1 INVENTOR. D/e/er 16 fmmermd/m BY c/o/Jn hf Dav/d3 [Val/ace E dob/7.9017

Aug. 24, 1965' D. K. EMMERMANN ETAL 3,202,343

COMPRESSOR ARRANGEMENT Filed May 16, 1962 5 Sheets-Sheet 2 INVENTOR D/e fer K Emma/19 mm BY c/o/7n H Day/d8 Waflace Eda/717cc g- 1965 I D. K. EMMERMANN ETAL 3,202,343

COMPRES SOR ARRANGEMENT Filed May 16, 1962 5 Sheets-Sheet 5 INVENTOR. O/e/er Kfk/me/ma'nfl BY c/a/m Daw'as /4 a//a Ge Eda/70501? ,f/h; KM/i/ Aug. 24, 1965 D. K. EMMERMANN ETAL COMPRESSOR ARRANGEMENT 5 Sheets-Sheet 5 Filed May 16, 1962 M 0 H 3 g a n S o l. 3 n 2 NN z a? n a m n a mr a wr W w w U 93W 3 m 3 p C 17 fie I T 2/ L c I 3 3 0 1 I!!! w w yaw M w 0 and discharge outlets.

United States Patent 3,202,343 COMPRESSOR ARRANGEMENT Dieter K. Emmermann, John H. Davids, and Wallace E. Johnson, Beloit, Wis., assignors to Desalination Plants (Developers of Zarchin Process) Limited, Tel Aviv, Israel, a limited company of Israel Filed May 16, 1962, Ser. No. 195,118 1% Claims. (Cl. 230-127) This invention relates to an improvement in fluid-displacement devices and more particularly relates to an improved fluid compressor provided for operation under subatmospheric pressure conditions. The apparatus of the present invention is hereinafter described in connection with a system for producing sweet water from sea water, but it must be appreciated that the present invention is capable of application in other fields.

Our associates and we have developed a system for desalination which produces large volumes of sweet water economically, and this is the subject of the copending United States patent application, Serial No. 103,114, filed April 14, 1961, now abandoned, for Methods, Systems, and Apparatus for Separating Solute in Substantially Pure Form From Solutions, which is hereby incorporated herein by reference.

This application relates to the construction and arrangement of a compressor which may be employed in this system. In this system sea water is flash-evaporated in a lowpressure evaporating chamber to form pure water vapor, pure ice, and concentrated brine. The compressor withdraws the vapor from that chamber and delivers it to a low-pressure condensing chamber where the vapor and ice and brought together to condense the vapor and simultaneously melt the ice to produce the final sea-water product.

As will hereinafter appear, a compressor of this type for use in vacuum-freezing systems must move and handle a large volume of vapor at low pressure, will be of great size and have a rotor which operates at high speed. The compressor is subject to low pressure at both its intake It is important that the impeller be as light as possible, because of the speed at which it operates.

Accordingly, an object of the invention is to provide a compressor of improved, simplified, economical construction.

A further object is to provide such a compressor which can operate under subatmospheric pressure conditions.

Another object is to provide an improved arrangement of a compressor, an evaporating chamber, and a condensing chamber for a vacuum-freezing system, for delivering vapor from the evaporating chamber into the condensing chamber.

Another object is to provide an improved compressor rotor assembly.

A still further object is to provide an improved compressor rotor assembly, including rotor blades of thin sheet material flexibly mounted on a central hub wherein the thin rotor blades assume operative positions due to centrifugal forces.

Another object is to provide an improved compressor rotor construction which can handle large volumes of vapor and yet is of relatively lightweight construction.

Another object of the present invention is to provide a new and improved method of assemblying rotor blades and rotor.

These and other objects and advantages will become more readily apparent as the description proceeds and is read in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic layout of a desalination system;

FIG. 2 is an enlarged fragmentary view in partial sec- 3,2@Z,343 Patented Aug. 24, 1965 J tion of the compressor and chambers arrangement of FIG. 1;

FIG. 3 is an enlarged fragmentary detailed view of the connection between the inducer rotor and blades of the inducer assembly of FIG. 2;

FIG. 4 is an enlarged fragmentary detailed view of a compressor rotor employed in the arrangement of FIG. 2;

FIG. 5 is a detailed side view of a pair ofinducer blades before bending thereof to seat the blades in the rotor hub;

FIG. 6 is a view in side elevation of an inducer blade blank from which the blades of FIG. 5 are formed;

FIG. 7 is a view in top elevation of the blades of FIG.

FIG. 8 is a view in section taken along line 8-8 of FIG. 5;

FIG. 9 is a view in section taken along line 9-9 of FIG. 5;

FIG. 10 is a View in section taken along line 1010 of FIG. 5;

FIG. 11 is a View in section taken along line 11-11 of FIG. 5;

FIG. 12 is a view similar to FIG. 6 illustrating a pair of compressor blades before bending thereof for seating in the rotor hub;

FIG. 13 is a fragmentary view of the inducer rotor with the blade blank of FIG. 5 bent to form a pair of blades having the common bight thereof disposed in the rotor;

FIG. 14 is a view in section taken along line 1414 of FIG. 13 illustrating the first step in contouring the blade common bight to the rotor;

FIG. 15 is a view similar to FIG. 14 illustrating the second step in contouring the blade bight;

FIG. 16 is a view similar to FIG. 14 illustrating the blade bight contoured to the rotor and locked in place; and

FIG. 17 is an enlarged fragmentary view in elevation illustrating the step of spreading the common bight of a pair of blades.

GENERAL DESCRIPTION OF SYSTEM The desalination system, with which the compressor of the present invention is used, is shown as a general layout in FIG. 1, the novel compressor being disposed in the upper central portion of FIG. 1. The general arrangement of this system will be first briefly described.

Sea water, which is at ambient temperature, and which has been filtered to remove floating material and other solids is brought into the system through sea water inlet pipe 10 and passes through deaerator 12 where dissolved gas is removed fromthe sea water. The sea water is then delivered by pump 14 to heat exchanger 16, where the incoming sea water is placed in heat-exchange relationship with the potable water final product and concentrated brine being withdrawn from the system.

The sea water entering the system will be normally at ambient temperature,'such as for example 77 F. and normally contains about 3.5% by weight of salt,

The sea water leaving heat exchanger 16 will be at a temperature of approximately 302 F. and is delivered through pipe 18 into the evaporating chamber 20. The sea water enters the evaporating chamber at the central hub of a distributor 22 (FIG. 2) and the water'thereafter flows downwardly over depending sheets on the distributor so that the incoming sea water has a large surface proportional to surface area.

the heat of vaporization is approximately 1074 Btu. per pound and the heat of fusion of ice is about 1144 B.t.u. per pound. As vapor is produced by evaporation, heat is removed from the remaining liquid and ice is formed therein. Due to the differences in heat of vaporation and heat of fusion, approximately 7 /2 pounds of ice will be produced for each pound of water vapor. The ice so produced is substantially pure water ice with no appreciable amount of salt contained therein. When continuous operation is established, the temperature within the evaporating chamber will be approximately 24.8" F. The vapor formed will be pure water vapor. Thus, upon removal of the pure water from the incoming sea water by the vaporizing and freezing, the remaining sea water becomes a more concentrated salt solution.

While theoretically in excess of 75% pure water by weight could be removed in the form of vapor and ice, we have found that removing approximately 50% by weight of pure water is in the range of greatest efiiciency; thus, if approximately 50% of the water is removed as vapor and ice, the remaining brine solution will consistof approximately 7% by weight'of salt.

The evaporation of water, with the consequent formation of vapor and ice, is a function of time since heat must be transferred, and also the rate of evaporation is In order to have the sea water remain in the evaporating chamber for a sufficient period of time and to otter large surface exposure of the sea water, a distributor means (not shown) is disposed within evaporating chamber 20.

The brine, with the ice crystals therein, is withdrawn from the bottom of evaporating chamber 20 through pump 24, and this mixture has a temperature of approximately 24.8 F. The mixture is delivered to separator washer or counter washer 26, in which the ice is separated from the concentrated brine and the ice is washed free of salt adhering to the surface of the ice crystals. The

' ice-brine mixture enters the lower end of the separatorwasher under pressure and the column of the separatorwasher becomes essentially full of ice crystals. The pressure exerted by the entrance of the brine at the bottom' of the counter washer forces the cylinder of ice packed therein upwardly, and this brine forces its way through the ice pack, out through screens 28. A pump 30 removes the brine from jacket 32 around the lower end of the counter washer. The pres-sure drop, created by forcing brine through the ice pack within the column, exerts a force on the column of packed ice moving it upwardly. Thus, the ice column within the counter washer continuously moves upwardly. At the upper end thereof is a motor-driven scraper r wiper 34 which wipes off the top of the upwardly moving column of ice and delivers the ice into trough 36. Spray heads 38 are provided at the top of count-er washer 26 for spraying sweet water supplied by pipe 40 onto the top of the porous column of ice, which water runs downwardly over the advancing column of ice to wash away any adhering brine on the surface or in the interstices of the ice.

Sweet water is added by means of pipe 42 to the icein trough 36 so as to produce a solution of sweet water and ice suspended therein which can be pumped.

By supplying sweet water to the ice to provide a liquid with the ice suspended therein, the resulting material may be more readily handled, and the liquor prevents the breaking of the vacuum within the vacuum The radial compressor generally indicated at 54, which forms the subject of this application, is positioned within the upper end of condensing chamber 50 and has an axial intake opening 56 in communication with evaporating chamber and a circular outlet 58 communicating with condensing chamber 50.

Vapor formed in evaporating chamber 20 is drawn into central inlet 56 of compressor 54 and delivered radially outward into condensing chamber 50 through outlet 58. The vapor is thus compressed and compressor 54 maintains condensing chamber 50 at a pressure of approximately 4.6 mm. Hg. The vapor delivered by the compressor into the condensing chamber passes downwardly on the compressor.

into contact with the ice disposed in trays (not shown) and simultaneously causes the vapor to condense and ice to melt. The sweet water thus produced is withdrawn from the lower end of condensing chamber 50 through pipe 60, which delivers a portion of the sweet water back to counter-washer 26 through pipes 40 and 42 for ice washing and for mixing with the ice. The majority of the sweet water product passes through pipe 62 to heat exchanger 16.

One of the greatest difiiculties encountered in prior art vacuum freezing systems is their inability to efliciently and economically handle and transport the large volumes of vapor that exist for any system producing a meaningful amount of sweet Water, particularly when it is recognized that we are dealing with such low pressures that approximately 4,500 cubic feet at vapor at these pressures is required to provide one pound of'water vapor. Without the arrangement and apparatus of this invention, expensive and extremely large compressors, shrouds and conduits would be required for handling the vapor. Normally, to move any such large volume, a multi-stage axial compressor would be required and the cost of the impellers and housings without considering the conduit size and expense would make the system uneconomical.

Additionally, by positioning the compressor within one of the chambers, the pressure differential across the shroud is so slight that a very inexpensive shrouding may be used In essence, the housing of the vessel into which the compressor discharges is the real structural support housing of the compressor.

Likewise, with the arrangement proposed, the compressor serves as a self-regulator upon the system since the amount of vapor that can be handled by the compressor will control the rate atwhich vapor is formed by vap0rization and the rate at which it is condensed.

Ideally, the vapor should be delivered to the evaporating chamber at saturation conditions of pressure and temperature so that the vapor will condense on the 32 F. ice will take out of the vapor 1,074 Btu. per pound of vapor condensed and thereby cause the 32 F. ice to melt by each pound absorbing 144 B.t.u. However, due to losses because of heat entering the system and superheating of heat into the system, and the drive mechanism between the motor and the compressor is of a unique type. Motor is flooded with water delivered to the motor housing by pump 72 through pipe 74 and this water is circuated through the motor housing and discharged through pipe 76. This drive mechanism provides an effective seal for the drive shaft of the compressor, withoutthe use of expensive and elaborate mechanical seals, which are normally required for such high pressure difierentials by allowing leakage of sweet water from the motor hous- 1ng into the condensing chamber. Sweet water flowing in the motor housing cools the motor and that portion of the sweet water leaking into the condensing chamber flash-evaporates to cool the compressed vapor and partially reduce the super-heat in the vapor.

As previously described, the final product, potable water, is delivered from condensing chamber 50 through pipe 62 to the heat exchanger 16 and is at a temperature of approximately 32 F. The concentrated brine which has been separated from the ice in counterwasher 25 is delivered Via pump 30 to the heat exchanger through pipe 78 and is at a temperature of approximately 24.8 F.

The purpose of the heat exchanger is to cool the incoming sea water to the maximum extent possible by withdrawing heat therefrom and delivering it to the cold brine and sweet water produced, and it is important that the sea water be cooled as efficiently as possible. With heat exchanger 16, approach temperatures of about 2 F. have been achievedand, thus, sea water entering the system through cold sea water pipe 18 is at about 302 F.

The sweet water, as it leaves heat exchanger 16 through pipe 80, is the principal product of this system and is delivered to storage tank 82 from which it may be withdrawn for use. The warmed concentrated brine, as it leaves heat exchanger 16 through pipe 84, is delivered to the waste outlet 68 for return to the sea or for other use or disposal.

It should be noted that a higher pressure is necessary in the condensing chamber than in the evaporating chamber because the vapor pressure of the freezing brine is lower than the vapor pressure of the ice-water mixture at 32 F. The vapor pressure of brine of 7% by weight salinity at 24.8 is about 3.2 mm. Hg, while the vapor pressure of ice-water mixture at 32 F. is about 4.6 mm. Hg. The

compressor maintains this condition.

It has been found advisable to recirculate a portion of the cold brine in order to prevent ice from building up within the evaporating chamber and thereby plugging the system and stopping continuous operation. Thus, a portion of the cold brine taken from counterwasher 26 is delivered by pump 30 into pipe 86, which connects with the distributor means (not shown) in chamber 20, which A suitable distribution means is shown in the copending U.S., application of John Hans Davids, Serial Number 85,522, filed Jan. 30, 1961, now Patent No. 3,103,792, the disclosure of which is hereby incorporated by reference herein. This introduction of concentrated brine with the sea Water does not interfere adversely with the evaporation and formation of vapor and ice, but conversely does prevent ice from building up on distributor 22. In addition, small ice crystals escaping from the drainage area of the counterwasher are thus reintroduced into the system to promote crystallization. Also, the greatest amount of ice is present in the ice-brine mixture at the bottom of evaporating chamber 22 and there is a tendency for ice buildup at that point. However, the introduction of additional brine increases the fluidity of the total mixture and also has a flushing action at the bottom of the evaporating chamber.

In any commercially successful desalination system, relatively large volumes of pot-able water must be produced and, while this may be effected by building larger and larger equipment, and, within shadow of commercial unacceptance due to high cost, the size of the equipment must be reasonable. With the system, schematically shown in FIG. 1, it is contemplated that approximately 60,000 gallons of potable water per 24 hour day would be produced.

' housing for the compressor.

6 Rather than attempt to increase the size of the equipment and thereby add to its expense out of proportion to gain, it is contemplated that when larger production of potable water is required, which will normally be the case, separate but parallel systems will be installed and operated to supply additional requirements.

By referreng to FIG. 2, it will be seen that compressor 54 is disposed within the outer housing of the condensingevaporating chambers. In the particular embodiment, the compressor is disposed immediately below cover 110 of chamber and above cylindrical walls 94 of evaporating chamber 20. The compressor is actually supported by this cover and comprises a housing or shroud 134, having a top housing 136 and a lower housing or shroud 138, which are preferably constructed of fiber glass and which are secured together but spaced apart around the periphery of the compressor by-attachment means 140. Bottom shroud 138 is provided with the previously mentioned central inlet 56, and the annular space between the top and bottom shrouds, extending completely around the compressor, provides the circular outlet 58 previously identified. Shrouds 136 and 138 are so sealed to the walls of the chambers that the only communication between the chambers is through central inlet 56, the interior of the compressor, and circular outlet 58.

Mounted within housing 134 on a common shaft is a rotating impeller 142 and a flow inducer 143 (FIG. 3) and it is important to note that this impeller is bearinged within and supported by the top cover 110 of condensing chamber 50. The housing 134 does not journal or support the impeller 142 and the housing is a lightweight shroud fully supported by cover 110, which with the other walls is the effective support and heavy-duty As seen in the drawings, the shroud or housing 134 is of thin, light construction. Impeller 142 comprises a plurality of pairs of radially extending blades 144, each pair having a common bight, and central hub 146 and is rotated bymotor 70 within housing 134. It must be appreciated that in order to move the volume of vapor required, this compressor is large and rotates at a relatively high speed. For example, the diameter of impeller 142 will be approximately 7 feet and the speed of rotation will be 3,600 r.p.m. For such speed of rotation and size of impeller, it is, therefore, most important that a strong and yet lightweight rotor be provided. Since cover 110 is a substantial structural member, it is able to afford the necessary shroud or covering for the impeller and is of relatively light material. In essence, the chamber into which the compressor is discharging serves here as the housing for the compressor and support for the drive.

While the system is operating and the compressor is rotating, vapor formed within evaporating chamber 20 is drawn into central'inlet 56, and is moved by rotating bladed inducer 143 and rotating blades 144 radially outward at progressively increasing pressure for ultimate discharge through circular outlet 58 into condensing chamber 50. In other words, the compressor affords a direct radial path for movement of the vapor. Important also is the fact that vapor will be drawn into the compressor throughout the entire area of central inlet opening 56 and discharged throughout the entire area of circular outlet 58. Thus, vapor will be delivered around the entire annular area of condensing chamber 50 for movement into contact with the ice that has been spread out within substantially the entire of the condensing chamber. With this concentric chamber and compressor arrangement, vapor will move from all points .of discharge from the compressor in a spiral path downwardly through the condensing chamber maintaining the high velocity imparted to the vapor by the compressor. Since condensation is afunction of surface contact and velocity of relative flow, this is, of course, advantageous. The advantages of the arrangement with regard to size and cost of equipment must be emphasized and apprepotable Water-producing system. mounted in the upper zone of the chamber 50 and overof the compressor.

ciated and this close-coupled relationship of the compressor and chambers accomplishes these advantages. if a conventional volute type casing for a compressor were utilized, its diameter would be about 14 feet and to convey the volume of vapor contemplated for the type of equipment shown, ducts having diameters of approximately 6 feet would be required. Equipment of this size obviously introduces thermal losses into the system and the cost of the parts and of insulation becomes substantial.

To a large degree vacuum freezing desalination systems have heretofore been penalized because of the failure to provide eflicient and economical equipment for and arrangements of the compressor and condensing and evaporating vessels. With the arrangements coni templated in the past to move such a large volume of vapor, one would normally use an axial compressor COMPRESSOR CDNSTRUCTION Referring first to FIG; 2, as before indicated, the presently improved compressor generally indicated at 54 is particularly suitable for use in the aforementioned Compressor 54 is lies the upper end of evaporating chamber 20 with its intake port 56 open to chamber 20. The compressor discharge outlet 58, peripherally thereof, is directly open to the condensing chamber 50.

As shown by FIG. 2, the compressor 54 is an axial h intake, raclial discharge unit of improved and compact construction.

It includes a two-part housing or casing 134 of metallic or non-metallic material, as suitable sheet metal of corrosion-resistant character or suitable plastic,

fiber glass, or other similar material, comprising an upper wall-forming member or housing 136 of circular periphery and a lower member or shroud 138, also of circular periphery and spaced from the upper member to form the rotor chamber 164 therebetween. Assembly connection of the members 136 and 138 is made by a plurality of attachment means and spacer elements 140 relatively spaced about the peripheral region of the housing in connection to the respective peripheral end portions 166 and 168 of the members.

.ber 138 is formed to provide a wall 1'70 of predetermined shallow frusto-conical form between the generally radial end portion'168 and an out-turned circular flange 172, the latter defining the axial inlet eye or intake port 56 The upper member 136 is formed to' provide a similar but oppositely directed shallow frusto-conicalwall section 174 inwardly from its generally radial end portion 166, merging into the inner wall section176 which lies in a radial plane normal to the rotor axis of the compressor. Thus, in sectional view (FIG. 2), the two wall sections 170 and 174 converge toward the discharge outlet 58 from a zone which, in the present example, is slightly radially beyond the inlet flange 172. While the described frusto-conical wall section 174 is preferred in member 136, this member could as by bolting at ltlil'to a plurality of tank strengthening ribs 182 depending from top wall 110. As shown in FIG. 2, the lower housing member 138 includes an ex ternal, depending annular flange 184 which seats in compressive engagement with resilient seal element 186, of rubber or the like, carried in an annular channel 187 on the outer overhanging margin 190 of the end wall 132 of chamber 20. Each rib 182 terminates in a lateral projection forming a pad against which the flange 1% of the compressor housing wall 134 abuts, such pad serving to effect the desired assembly location of the wall. Due to the vacuum .in the chambers, considerable load will be exerted on cover 110 to cause deflection thereof, but since compressor 54 is supported and carried thereby, no problems to the compressor result from this deflection.

Referring to FIGS. 2 and 4, operative in the housing as above described is a compressor rotor assembly or rotatable impeller 142 comprising a hub structure 146 on a vertical drive shaft 196, and a plurality of generally radial blades 144, constructed in accordance with the present invention, projecting from the hub. The hub structure comprises a shaft-mounting sleeve hub 198 keyed to, pressed on, or otherwise fixed to drive shaft 196' and held thereon as by a retainer plate 200 bolted to the shaft, and a blade hub 202, here shown constructed in one piece, secured as by bolts 204 to the I flange portion 206 of shaft hub 198.

Referring to FIGS. 2 and 4, formed in the hub 202 are a plurality of circular through bores 208 parallel to the shaft axis, these being inwardly adjacent to the hub periphery and equi-angularly spaced circumferentially of the hub. Each bore 208 has a radial slot 210 of predetermined width, opening the bore to the hub periphery, the slots as well as the bores being open at each side face 212 of the hub. The bores and slotsform blade mounting seats.

Each blade 144 is formed from a strip of flexible sheet material having a predetermined thickness. The blade material here used is fiber glass, or corrosion-resistant metal, as stainless steel or the like. In blade formation, an elongate rectangular strip of predetermined'length and width, exemplary dimensions being shown on'the drawing, is lengthwise reversely turned or folded upon itself, folding being about a round bar or arbor (not shown) at the strip center, to provide a pair of blades 144 having a common bight or a hollow circular enlarged or eye portion 218 at one common end. Each pair of blades over their outer end section 222 (FIG. '12) is marginally cut or reduced on one side to provide a blade margin 224 such that the blade will have a running clearance in the converging zone of the compressor housing formed by the wall portions and 174, FIG. 2.

As appears in FIG. 2, there is preferably mounted to the hub 146, as by bolts 298 for rotation therewith an inducer rotor hub 300. The inducer hub 300 is provided with a plurality of circular through bores 302 extending parallel to the shaft axis and being inwardly adjacent to the hub peripherally and equi-angularly spaced circumferentially of the hub. Each bore has a radial slot 304 of predetermined Width opening the bore to the hub periphery, the slots as well as the bores being open at each side face 306 of the hub (FIG. 3). The bores and slots form inducer blade mounting seats.

A pair of inducer blades 308 and 310 are formed from a flexible single stock blank of strip sheet material (FIG. 6), such as metal or a plastic fiber glass material, having a predetermined thickness and contour (FIGS. 3, 611, and 13). The strip of sheet material is bent around a round bar or arbor (not shown) at the strip center to form a common bight 311 (FIG. 13) and thereby provides a pair of blades '(FIG. 3) having an enlarged common eye portion at one end. An inducer The inducer blades are preferably provided with a bucket shape for efficient operation thereof. To this end, the outer ends 318 of each blade 308 and 310 are pre-formed before bending of the stock strip (FIG. 6) to provide the bucket shape thereto. The strip 312 is bent at a plurality of locations at predetermined angles at each end thereof substantially along the dotted lines shown in FIG. 6 to provide flanges defining the desired bucket shape. For example, referring to FIGS. 6 and 8, a strip 312, having the exemplary dimensions shown in FIGS. 5-7, may be bent along line 8-8 of FIG. 6 and at the angle indicated in FIG. 8 to provide the flange 316 with the dimensions indicated in FIG. 8. Similarly the strip may be bent at other locations as indicated in FIGS. 9, 10 and 11 at locations shown in FIG. 6 and at the angles indicated in these figures to provide the flanges 316 with the dimensions noted in these figures. It will be appreciated, of course, that the dimensions given are exemplary only and that, depending upon the requirements of the rotor arrangement desired, these parameters of the inducer blade may be determined by employment of known computation methods.

After the flanges 316 have been formed on the strip 312 at each end thereof, the strip 312 may be bent at its center around an arbor (not shown) to form the two blades 308 and 310 having the common bight 311 (FIG. 13).

Secured to the inducer rotor by bolts 298 (FIG. 2) is a mounting plate 318 for a rod 320 which carries a semi-hemispherical shell 322 of rigid material, such as fiber glass or stainless steel. The shell is centrally carried near the top of the chamber 20 and serves as a streamline surface which cooperates with the inducer arrangement of the present invention to direct the flow of vapor from chamber 20 to the impeller of the compressor.

BLADE MOUNTING ARRANGEMENT The compressor blade mounting arrangement is similar in construction to the inducer blade mounting arrangement, and, thus, the description to follow of the inducer blade mounting arrangement, it will be appreciated, applies equally to the description of the impeller blade mounting arrangement.

After each of the strips 312 has been bent upon itself to form a pair of blades 308 and 310 having a common bight 311, the bight of each pair of blades is longitudi nally inserted in a bore 302 of the blade hub 300 in such a manner that the blades 308 and 310 extend through the corresponding slot 304 in the hub 300 (FIG. 13). It will be observed that the bight 311 of the blades 308 and 310 is of lesser dimension than the bore 302. Such sizing of the bight 311 facilitates contouring of the bight to the bore 302 and permits expansion of the bight to the dimension of the bore.

To contour and expand the bight, a tapered tap tool 322 (FIG. 14) is forced from the top or bottom of the rotor 300 into the space defined by the bight 311 to spread and contour the bight. The tap tool 322 is provided with a tapered elongated conical portion 323 which is inserted first into the space defined by the bight 311 and is also provided with a head 324 of cylindrical external configuration which is of a diameter corresponding generally to the diameter of a removable pin 326 (FIG. 15) which is employed to secure the common bight in the bore and to prevent lateral translation of the blades 308 and 310.

After the head 324 of the tool 322 has been forced into the space defined by the bight to spread the bight and to force it in contact with the wall of the hub 300 defining the bore 302, the hollow pin.326 (FIG. 15 is placed on top of the head 324 and forced into the space occupied by the head 324 which results in removal of the tool 322 from the said space. The hollow pin 326 is forced into the spaced defined by the inner surface of the bight 302 until the top surface 327 and bottom surface 328 of the pin are flush with the corresponding surfaces 301 of the hub 300 as appears in FIG. 16.

With the pin 326 in the position shown in FIG. 16, the blades 308 and 310 assume the position shown in dotted lines in FIG. 17.

Experience has indicated that pairs of blades constructed in accordance with this invention and employed for moving large quantities of vapor under vacuum conditions had a short use life because the blades had a tendency to break at the points a (FIGS. 3, 13 and 17) Where the radius R of the blade bight curves to join the blades 308 and 310. This experience was obtained as the result of employing only the pin 326 to seat the pair of blades, and if one of the blades broke, the other blade would, due to the forces acting thereon, pull out of the seat during operation of the assembly.

A feature of the present invention resides in the provision of means for initially contouring the blades at points a to correspond to arcuate surfaces 330 of the webs 332 defined by adjacent bores 302 and by the provision of strengthening means hereinafter described which are employed to maintain the blades contoured at points a during operation of the impeller and inducer assemblies. Means for initially contouring the blades at points a to the arcuate surfaces 330 may take the form of a wedging tool, generally indicated by the numeral 334 in FIG. 17, and which comprises a handle 336 and a head 338. The head 338 is provided with a concave outer surface 340 having a curvature corresponding to the outer curvature of the pin 326 against which the surface 340 is designed to rest. The side walls 342 and 344 of the head 338 are convergingly tapered and of a width dimension corresponding to the width dimension of the blades 308 and 310. In use, the tool head is inserted between the blades 308 and 310 when in the positions shown in dotted lines in FIG. 17 and the tool pushed inward to spread the blades 308 and 310 until the head surface 340 engages the outer surface of the pin 326, as shown in full lines in FIG. 17. When the surface 340 engages the pin 326, the side walls 342 and 344 of the head 338 spread the blades 308 and 310 and in so doing bend and contour the blades at points a to the configuration of the arcuate surfaces 330 of the webs 332.

The tool head 338 is removed from contact with the pin 326 and after removal of the tool, the blades will have a pro-formed contour at points a.

The means for maintaining the blades in position with the common bight seated in the bore of the rotor hub may, in accordance with the present invention, take the form of a U-shaped wedge shoe 346 (FIG. 3) of a length corresponding to the thickness of the hub 300. The shoe 346 is provided with an arcuate body portion 348 and depending parallel flanges 350 and 352. The flanges each have an edge in line contact with pin 326 when the shoe is removably secured to the pin 326 by a screw 354 threaded through an aperture in the shoe 346 and through a corresponding aperture 356 in the pin 326. The shoe 346 spreads the blades 308 and 310 when in threaded engagement with the pin 326 in such a manner that the side Walls 358 and 360 of the flanges 352 and 350 urge the blades 308 and 310 against the webs 332 and cooperate with the pin 326 and webs 332 at points a to maintain the blades at these points in contact with the arcuate surfaces 330 of the webs 332.

With the shoe arrangement shown in FIG. 3, the blades do not have a tendency to break at points a during the normal expected use life of the compressor assembly.

To further strengthen the blades at the roots thereof and to minimize the effects of vibration on the blades at the roots thereof during operation, a plurality of U-shaped damping clamp wedge members 364 are employed around the periphery of the hub 300, Where, for example, sixteen bores are formed in the hub thus providing for employment of sixteen pairs of blades 308 and 310.

The wedge members 364 are U-shaped or wing-shaped ill in configuration and comprise a body portion 366 in engagement with the body 348 of the shoe 346. The body has extending therefrom flexible flanges 367 and 368.

The flanges 367 and 368 each engage the inner surfaceof the blades 308 and 310, respectively. The Wedge member 364 is preferably secured in engagement with the shoe 346 by means of the screw 354 passing through a threaded aperture in the body portion 366 thereof. When in the position shown in FIG. 3, the flanges 367 and 368 maintain the blades 308 and 310 in spaced-apart relation. A plate 37% may be employed to distribute the pressure applied to the wedge during threading of the screw 354. The wedge members 364 may be constructed of sheet material formed with the flanges 367 and 368 and bored and threaded for receiving the screw 354.

It will be observed that the wedge members 364 are designed to dampen out the effects of vibrations on the blades 3% and 31th A plurality of second clamping clamp wedge members 372, corresponding to the configuration of the wedge members 364, are provided with a body portion 374 and flexible flanges 376 and 378. The body portion 374 is apertured and threaded to receive a threaded screw 330 which secures the wedge member 372 to the web 352 which is bored and threaded to receive the screw 380. It will be observed that the flanges 376 of the wedge members 372 cooperate with the adjacent flanges 368 of the wedges sm to support the blades 31!) adjacent the common bight 311. Similarly, the flanges 378 of the wedge members 372 cooperate with the adjacent flanges 367 of the wedges 364 to strengthen and support the blades 3% adjacent the common bight 311. It will be appreciated that the plurality of alternative first Wedge members 3&4 and second wedge members 372 positioned around the periphery of the hub 360 cooperate to provide a blade support and strengthening arrangement for a plurality of pairs of blades 368 and 310, each pair having a common bight 311. A plurality of plates 332 and 384 may be provided for distributing the force applied to body 374 of the wedge members 372 by the screws 38h.

To complete the mounting of the pairs of blades 398 and 31% in the bores 32%, pipe plugs (not shown) may be threaded into the ends of the pins 326 (FIG. 16) and the pins may be provided with slots 3% for expansion thereof by the pipe plugs to lock the blades in position.

Referring to FIGURE 4, it will be observed that the same blade mounting arrangement and strengthening means are employed for the compressor hub 7.02 and rotor blades 14-4. The blades 144, as aforesaid are formedin pairs having a common bight, are flat, and do not have flanges 316.

In assembling the blades of the compressor to the hub 292, as appears in FIG. 4-, each pair of blades has a common enlarged end, or eye 218 inserted and seated in one of the hub bores 2% with the blades projecting outwardly therefrom through the associated bore slot 210. The outer diameter of the common bight or blade eye 218 is such as to effect a snug fit thereof in the bore, while the width of the bore slot 21% is such as to closely confine the blade portions extending therethrough. The webs 395 (FIG. 4) of the hub are provided with an arcuate surface 397 at points a and the blades are bent at these points as indicated above in connection with the description of the mounting of the inducer blades 3% and 31%. Pipe plugs (not shown) may be employed to close the ends of the pins 326 having the slots 3% therein.

The blades 144 thus mounted on hub 202 extend therefrom in the compressor housing rotor chamber 164 with the reduced or convergingly tapered end portions 224- thereof in close running fit in the converging zone of the housing provided by walls 170 and 174. These rotor blades M4, being'constructed of thin sheet strips in the manner described, afford lightweight flexible blades which, mounted as shownand described, permit highspeed operation of the rotor. The blades have a predetermined minimum thickness as, for example, ap proximately two hundredths of an inch (.02 inch) in a blade having a length of about thirty one (31) inches and a width of about nine (9) inches inwardly of its tapered end. This minimum thickness is sufficient for structural self-support of the blades in displacing water vapor under the heretofore indicated sub-atmospheric pressures, as the blades being flexible, will assume positions of radial extension from the hub under the influence of centrifugal forces thereon in compressor operation. Thus, the improved rotor structure is one which will be economically constructed with easy-to-fabricate blades and a simple yet highly eficient blade-mounting and damping arrangement. The thin blades formed in the manner described, facilitate desired high-speed rotation of the rotor under vacuum conditions and such high-speed operation is further facilitated by the absence of rotating blade shrouds.

The compressor as herein illustrated and now described is designed and fully effective for handling water vapor in large amounts and at a relatively low compression ratio, under the desired sub-atmospheric conditions. In this construction, the opening sides or diameter of the compressor inlet eye 56 is determined-in accordance with the desired velocity of vapor intake and flow rate in the compressor. As illustrated in the present example, the inlet is of relatively large diameter and open to the blades over approximately the inner half lengths there- 0 pendent on rotor speed and the outer diameter of the rotor blading, these factors are selected to obtain the desired compression ratio suitable to the purpose of the system referred to. A compressor constructed in accordance with the present invention under operating conditions is required to move approximately two hundred thousand ft. vapor per minute to obtain sixty thousand gallons per day of the final product, sweet water.

It will be observed that the weight of the compressor assembly is relatively light when compared to comparable compressor assemblies. Moreover, the rotor, itself, serves as a tool in the formation and mounting of the pairs of blades, which formation would be otherwise diflicult to achieve because of the high-spring back characteristics of the material employed for blade construction. Preferabl', the rotor hubs and the pin 326 are plated with a corrosive resistant material, such as tin. It will also be appreciated that with the present invention the area of greatest cost of manufacture, i.e., blade construction and mounting to the hub, has been minimized.

It is to be noted that the straight peripheral portions or margins 166 and 168 of the compressor housing, defining the compressor outlet 58 which is open circumferentially of the compressor, forms a diffuser wherein the dynamic energy ofthe discharged vapor is converted to static pressure. Such diffuser may be extended to form a con tinuation of the compressor housing wall member 138 and, cooperating with the adjacent top portion 110, provides a downwardly directed annular outlet into condensing chamber 5i).

From the foregoing, it will be seen that the compressor and compressor rotor are of extremely simple, compact and emcient construction and yet economical incest and high speed in operation.

The rotor assembly has blades of thin sheet material in a flexible mounting on' a central hub and can handle large volumes of vapor at a relatively low compression ratio under the given sub-atmospheric pressure conditions with the blades assuming operative positions responsive to centrifugal force.

Although the present application describes the presently preferred embodiment of this invention and is shown in connection with the system of producing potable water fromsea Water, it will be appreciated, of course, that the present invention has utility in other applications.

Also, since the degree of vapor compression is dea 13 Although various minor modifications of the present invention will become readily apparent to those versed in the art, it should be understood that what is intended to be covered by the patent granted hereon are all such embodiments as reasonably and properly come within the scope of the contribution to the art hereby made.

We claim:

1. In a low pressure system for moving a fluid at high speed from a first low pressure compartment into a second low pressure compartment which is maintained at a higher pressure than said first compartment, a compressor arrangement adapted to be disposed between said compartments with an inlet opening into said first compartment and an outlet opening into said second compartment, said compressor including a rotatable hub carrying at least one pair of flexible, elongated blades of thin cross section, said hub being provided with a bore extending parallel to the axis of rotation of the hub, said bore opening to the periphery of the hub, each compressor blade being joined to another compressor blade to form a pair of blades having a common bight portion, said common bight portion of said pair of blades being seated in the bore with the pair of blades extending through the opening of the bore, and means for mounting the common bight portion of said pair of compressor blades to said compressor, said mounting means incuding a pin in the space defined by the common bight portion for urging the bight portion against the wall of the bore and a shoe member positioned between the pair of blades and disposed partially in said slot for maintaining the blades in spaced relation, said pin and corresponding shoe member cooperating to hold the pair of blades to said hub.

2. The improvement of claim 1 wherein said shoe member is mounted to said pin.

3. The improvement of claim 1 including means for strengthening the pair of blades adjacent the bore opening of the hub, said strengthening means being located between the blades and secured to the hub.

4. The improvement of claim 3 wherein said strengthening means includes a first wedge member located between said blades for urging the pair of blades in spaced relation to each other, said "wedge member cooperating with said pin to hold said pair of blades to said hub.

5. In a low pressure system for moving a fluid at high speed from a first low pressure compartment into a second low pressure compartment which is maintained at a higher pressure than said first compartment, a radial compressor arrangement adapted to be disposed between said compartments with an inlet opening into said first compartment and an outlet opening into said second compartment, said radial compressor including a rotatable hub carrying a plurality of flexible, elongated blades of thin cross-section, a two-part housing comprising a first wall forming member and a spaced second wall forming member, the second member having an intake port adapted to open directly into said first compartment, the compressor blades being carried by the hub in the space between said members, said outlet of said compressor being the space between said members defined by the peripheries of said members, said outlet adapted to open directly into said second compartment, each of'said compressor blades be ing joined to another compressor blades to form a pair of blades having a common bight portion, said bight portions being carried by said compressor hub, said hub having a plurality of spaced bores extending parallel to the axis of rotation of the hub and opening to the periphery of the hub, each common bight portion of a pair of blades being seated in one of said bores with the pair of blades extending through the opening of the bore, and means for mounting the common bight portion of each pair of said compressor blades to said compressor hub, said mounting means including a pin in the space defined by the common bight portion of each pair of blades for urging the bight portion against the wall of the hub defining the bore and a shoe member positioned between each pair of blades having a common bight portion for maintaining the pair of blades in spaced relation, said pin and corresponding shoe member cooperating to hold the corresponding pair of blades to said hub.

6. The improvement of claim 5 wherein each shoe member is mounted to the corresponding pin.

7. In a low pressure system for moving a fluid at high speed from a first low pressure compartment into a second low pressure compartment which is maintained at a higher pressure than said first compartment, a compressor arrangement adapted to be disposed between said compartments with an inlet opening into said first compartment and an outlet opening into said second compartment, said compressor including a rotatable hub carrying a plurality of flexible elongated blades of thin crosssection, and a bladed inducer rotor having an inducer hub axially aligned with the compressor hub and located between said compressor hub and the inlet opening to said first compartment, said inducer blades being elongate and of thin cross-section, at least two of said inducer blades being joined to form a common bight portion, said inducer hub being provided with a bore extending parallel to the axis of rotation of the inducer hub and opening to the periphery of the hub, said common bight portion of said pair of inducer blades being seated in the bore with the pair of inducer blades extending through the opening of the bore, and means for mounting the common bight portion of said pair of inducer blades to said inducer hub, said mounting means including a pin in the space defined by the common bight portion for urging the bight portion against the wall of the bore and a shoe member positioned between the pair of inducer blades and mounted to said pin for maintaining the pair ofinducer blades in spaced relation, said pin and shoe member cooperating to hold the pair of inducer blades to said inducer hub.

8. The improvement of claim 7 wherein said shoe member is mounted to said pin.

9. A rotor assemblyadapted for moving a fluid at high speed comprising a rotor having a hub and a plurality of pairs of flexible blades, each of said pairs of blades having a common bight portion mounted to said rotor hub,

said rotor hub having a plurality of spaced bores, each of said bores having a slot opening the bore to the periphery of the rotor hub, one of said pairs of blades extending through the slot opening of each of said bores with the common bight portion thereof seated in said bore, means carried by the hub between each pair of blades having a common bight portionfor maintaining each pair of said blades having acommon bight portion in spaced-apart relation and means for strengthening each of said pairs of blades adjacent the corresponding bore opening of the rotor hub.

10. A rotor assembly adapted for moving a fluid at high speed comprising a rotor having a hub and a plurality of pairs of flexible blades, each of said pairs of blades having a common bight portion mounted to said rotor hub, said rotor hub having a plurality of spaced bores, each of said bores having a slot opening the bore to the periphery of the rotor hub, one of said pairs of blades extending through the slot opening of each of said bores with the common bight portion thereof seated in said bore, means carried by the hub between each pair of blades having a common bight portion for maintaining each pair of said blades having a commonbight portion in spaced-apart relation, said means including a plurality of shoe members carried by the hub, one of said shoe members being disposed between the blades of each of said pairs of blades, and a pin disposed in the space defined by each of said common bight portions for contouring the bight portion and for securing the bight portion in its hub bore.

11. The assembly of claim 10 wherein each of said shoe members is secured to the corresponding one of said pins.

high speed comprising a rotor 12. A rotor assembly adapted for moving a fluid at high speed comprising a rotor having a hub and a plurality of pairsof flexible blades, each of said pairs of blades having a common bight portion mounted to said rotor hub, said rotor hub having a plurality of spaced bores, each of said bores having slot opening the bore to the periphery of the rotor hub, one of said pairs of blades extending through the slot opening of each of said bores with the common bight portion thereof seated in said bore, means carried by the hub between each pair of blades having a common bight portion for maintaining each pair of said blades having a common bight portion in spaced-apart relation, said means including a plurality of shoe members carried by the hub, one of said shoe members being disposed between the blades of each pair of said pairs of blades, and means for strengthening each pair of said pairs of blades adjacent the corresponding bore opening of the rotor hub, said strengthening means including a plurality of first wedge members, one of said wedge members being disposed between each pair of blades having a common bight portion, said wedge members cooperating with the corresponding shoe members to maintain the adjacent pair of blades having a common bight portion in spaced apart relation.

13. The assembly of claim 12 wherein said strengthening means includes a plurality of second wedge members carried by the rotor hub, each of said second wedge members being mounted to the rotor hub in a location between two of said first wedge members and in contact with sides of two blades of two different pairs of said blades, said sides being opposite the sides of said blades contacted by the corresponding first wedge members, said second wedge members cooperating with said first wedge members and said shoe members to hold and strengthen the blades therebetween adjacent the bores of the rotor hub.

14. A rotor assembly adapted for moving a fluid at hub and at least one pair of rotor blades having a common bight portion mounted to said rotor hub, said blades being flexible and formed from a strip of flexible sheet material bent lengthwise 'upon itself at approximately its center to define said common bight portion, said common bight seated in a bore formed in the rotor hub with said pair of blades extending through a slot opening the bore to the periphery of the rotor hub, means at least partially portion being disposed in said slot and carried between said blades for maintaining said blades in spread-apart relation, and means for strengthening the pair of blades adjacent the bore opening of the rotor hub, said strengthening means being located between pairs of blades and between blades of pairs of blades.

15. A rotor assembly adapted for moving a fluid at high speed comprising a rotor hub and at least one pair of rotor blades having a common bight portion mounted to said rotor hub, said blades being flexible and formed from a strip of flexible sheet material bent lengthwise upon itself at approximately its center to define said common bight portion, said common'bight portion being seated in a bore formed in the rotor hub with said pair of blades extending through a slot opening the bore to the periphery of the rotor hub, means at least partially disposed in said slot and carried between said blades for maintaining said blades in spread-apart relation, said means for spreading said blades including a shoe memhas ber disposed between said blades and mounted to said rotor hub for maintaining said pair of blades in spaced apart relation, and means for strengthening the pair of blades adjacent the bore opening of the hub, said means including a first wedge member which is disposed between the blades and which cooperates with the shoe member to maintain the pair of blades in spaced apart relation, said shoe member being positioned at least partially in said slot.

16. A rotor assembly adapted for moving a fluid at high speed comprising a rotor hub and at least one pair of rotor blades having a common bight portion mounted to said rotor hub, said blades being flexible and formed from a strip of flexible sheet material bent lengthwise upon itself at approximately its center to define said common bight portion, said common bight portion being seated in a bore formed in the rotor hub with said pair of blades extending through a slot opening the bore to the periphery of the rotor hub, and means at least disposed in said slot and carried between said blades for maintaining said blades in spread-apart relation, said means for spreading said blades including a shoe mem ber disposed between said blades and mounted to said rotor hub for maintaining said pair of blades in spacedapart relation, and a pin in the space defined by the common bight portion for contouring the bight portion and for securing the bight portion in the bore, said shoe member and pin cooperating to hold said pair of blades to said hub. i

17. The assembly of claim 15 wherein said strengthening means includes a pair of second wedge members carried by the rotor hub on the sides of the blades opposite the sides of the blades contacted by the shoe member, said second wedge members cooperating with said first wedge member and said shoe member to hold the blades 'therebetween adjacent said bore.

18. The assembly of claim 16 wherein said shoe member is secured to said pin.

References Cited by the Examiner UNITED STATES PATENTS 881,409 3/08 Jude 25377 1,035,364 8/12 Leblanc l03.-1l5 1,426,954 8/22 Brooks 103-1l5 1,880,665 10/32 Barker 230-133 2,114,780 4/38 Juelson 230ll7 2,579,583 12/51 Johnson 29156.8 2,620,554 12/52 Mochel et al. 29l56.8 2,638,663 5/53 Bartlett et al. 29156.8 2,652,191 9/53 Buchi 230134 2,656,146 10/53 Sollinger 253-'77 2,656,973 10/53 Sutherland 230-117 2,889,107 6/59 Stalker 230- 419 FOREIGN PATENTS 561,554 10/57 Belgium. 614,971 9/55 Canada. 332,859 7/30 Great Britain. 662,517 12/ 51 Great Britain. 787,500 12/57 Great Britain.

KARL I ALBRECHT, Primary Examiner.

ROBERT A. OLEARY, JOSEPH H. BRANSON, JR.,

0 Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,202,345 August 24, 1965 Dieter K. Emmermann et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 33, for "and", first occurrence, read are column 4, ijiine 51, after "ice" insert and the ice column 6, line 66; after "entire" insert area column 1 line 16, for "the seat during operation of the assembly" read its seat during operation of the assembly Signed and sealed this 5th day of April 1966.

SEAL) .ttest:

RNEST W. SWIDER EDWARD J. BRENNER testing Officer Commissioner of Patents 

1. IN A LOW PRESSURE SYSTEM FOR MOVING A FLUID AT HIGH SPEED FROM A FIRST LOW PRESSURE COMPARTMENT INTO A SECOND LOW PRESSURE COMPARTMENT WHICH IS MAINTAINED AT A HIGHER PRESSURE THAN SAID FIRST COMPARTMENT, A COMPRESSOR ARRANGEMENT ADAPTED TO BE DISPOSED BETWEEN SAID COMPARTMENTS WITH AN INLET OPENING INTO SAID FIRST COMPARTMENT AND AN OUTLET OPENING INTO SAID SECOND COMPARTMENT, SAID COMPRESSOR INCLUDING A ROTATABLE HUB CARRYING AT LEAST ONE PAIR OF FLEXIBLE, ELONGATED BLADES OF THIN CROSS SECTION, SAID HUB BEING PROVIDED WITH A BORE EXTENDING PARALLEL TO THE AXIS OF ROTATION OF THE HUB, SAID BORE OPENING TO THE PERIPHERY OF THE HUB, EACH COMPRESSOR BLADE BEING JOINED TO ANOTHER COMPRESSOR BLADE TO FORM A PAIR OF BLADES HAVING A COMMON BIGHT PORTION, SAID COMMON BIGHT PORTION OF SAID PAIR OF BLADES BEING SEATED IN THE BORE WITH THE PAIR OF BLADES EXTENDING THROUGH THE OPENING OF THE BORE, AND MEANS FOR MOUNTING THE COMMON BIGHT PORTION OF SAID PAIR OF COMPRESSOR BLADES TO SAID COMPRESSOR, SAID MOUNTING MEANS INCLUDING A PIN IN THE SPACE DEFINED BY THE COMMON BIGHT PORTION FOR URGING THE BIGHT PORTION AGAINST THE WALL OF THE BORE AND A SHOE MEMBER POSITIONED BETWEEN THE PAIR OF BLADES AND DISPOSED PARTIALLY IN SAID SLOT FOR MAINTAINING THE BLADES IN SPACED RELATION, SAID PIN AND CORRESPONDING SHOE MEMBER COOPERATING TO HOLD THE PAIR OF BLADES TO SAID HUB. 